Yes, this is more what I'm trying to get at. I am speaking specifically in terms of branch circuits such as those feeding various auxilliaries, compressor, lighting, control, door circuits, etc. You will note that even on this diagram, the body lighting switch is indeed ahead of the fuse. In fact, if you look at most branch circuit wiring diagrams for cars and compressors in particular, you will see that the switch is almost always ahead of the fuse which is why I am questioning why this is not the case with this car.

In the "good old days" motormen were often called upon to change out fuses, lamps and even trolley poles, in some cases. Cars often carried carried spare lamps fuses and most of our heritage cars have some form of ladder or step arrangement to get to the roof. Today, I presume most (if not all) systems require a "pull in to the carhouse to change a bent / damaged pole or blown roof fuse. but in my time, this was routinely done out on the road by mechanics.

Speaking as a trolley guy, the more I read the National Electrical Code, the less I know about electricity. LOL!

This is why electrical inspectors and the NEC are not welcome inside railroad cars, nor in the DC part of any substation. "Yes, there's a bleedin REASON we want ungrounded 480, I don't care what the code says."

For instance on a diesel locomotive, the battery circuits are grounded, and the 600V circuits are intentionally isolated from ground. On Westinghouse HB equipment, the traction circuits are grounded by necessity because the current return is the rails... and the battery circuits are intentionally isolated from ground. This is to keep the battery circuits from being used as a return path by traction power between cars. You explain any of this to a code electrician and his brain is going to explode. DC is not AC and the railroad environment is unique.

OT...but may as well.
HEP still confuses me a little. It's delta 480 right? Is it all isolated from ground? What about the after-transformers 120/208 on board a car? Floating or grounded? I'm curious what effect if any the lack of a wired neutral on the 480 side can have via the running rails, especially as the train traverses an insulated joint and if it can have an effect on signals. I'm assuming no but not sure why not.

Steve

[quote="robertmacdowell"][quote="6-18003"]Ah. The more I learn about trolley
For instance on a diesel locomotive, the battery circuits are grounded, and the 600V circuits are intentionally isolated from ground.

This is only true on industrial locomotives with main generators of the 250 volt variety. I don't know about 100 ton GE's but all smaller models have are battery negative ground. On EMD, GE and Alco switchers and road locomotives, both the high voltage and the battery voltage are isolated from "ground". Low voltage grounds can drive the MU circuits and electrical folks nuts.

Howard

There's no such thing as neutral with 480 delta. Doesn't exist. (ok there are some wacky setups where one of the three phases is defined as neutral, e.g. the Italian electrifications, but it's not common at all.) I would think that if Amtrak 480 was leaking enough to the carbody to affect a signal, that would be considered a ground fault.

If you want neutral with your 480, that's what 480 wye is all about. Neutral in the middle, and 277V between neutral and any phase. If you have a machine that wants 480 wye, you just don't connect the neutral.

208 is by definition "wye", since it is defined as 120 between the neutral and any phase. So yes at that point you would be grounding the neutral to the carbody, presumably.

So if the 480 is fully floating no leg has any voltage relative to ground?

Steve

For the record, the battery circuits on "most" small GE diesels (such as the 1953 model 25 tonner I'm now working on at Pennsylvania Trolley Museum) are grounded on the positive side, the opposite of the practice on most vehicles. The high voltage side is not grounded.

One question that arose w/r to the PTM loco during the installation of AC wiring for a block heater and battery charger is whether or not to connect the AC ground (not the neutral, but the earth ground) to the loco frame. This is because it will be used on electrified trackage at PTM and there was doubt as to the wisdom on connecting the AC ground to the DC ground (the rails) of PTM's 600VDC trolley supply. The discussion is on-going.

While the trolley lighting circuit here discussed has some interesting features, any circuit that raises the voltage on some lamps when one fails has the basic disadvantage of being subject to a "runaway" if successive lamp failures occur before the first one is repaired. I have witnessed the 20 lamp series lighting circuit on a PCC perform such a failure. There were several lamps already out resulting in the remainders burning noticeably brighter. Then one more went....then another, and suddenly all of the remaining lamps began to go in quick succession. At that point the fuse in the circuit opened, saving at least some of the lamps, but at least half of them had blown by then.

"This is only true on industrial locomotives with main generators of the 250 volt variety. I don't know about 100 ton GE's but all smaller models have are battery negative ground."

Attached is the diagram for a 1000hp Ge 100 tonner. External battery charger is simply hooked to the right side of the open battery switch and removed before the switch is closed.

[quote="David H. Hamley"]For the record, the battery circuits on "most" small GE diesels (such as the 1953 model 25 tonner I'm now working on at Pennsylvania Trolley Museum) are grounded on the positive side, the opposite of the practice on most vehicles. The high voltage side is not grounded.
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That's interesting. I checked our locomotives today and the 44 ton GE, 65 ton GE and 80 ton GE all have negative ground battery systems. However, as you say, the 25 ton and (according to the GE service manual) 45 ton models have positive ground systems. Plus, they gave the 65 ton a 32 volt system like the 45 ton. It seems that GE could not make up their minds.

Howard

A further comment on the battery polarity of small diesels, if only to illustrate the diversity involved, is that Pennsylvania Trolley Museum's 1942 Porter 43 ton center cab has two 32V battery sets. Units built for the Navy were often so equipped. But you can't run one of the engines without the opposite battery bank being energized because the fuel shut off solenoids on BOTH engines are wired to one battery bank only. The last owner of the loco prior to the museum resolved this by installing a tie switch that puts both battery sets in parallel.

In this loco, neither side of the battery is grounded. This is likely typical of small locos with Westinghouse Electric-designed systems. But never assume that all Porters (and Whitcombs, Davenports, Vulcans, etc.) have Westinghouse systems. There were GE equipped examples from all the small builders.

Thus the RULE: Assume nothing.

Different markets. The 44 is aimed at the mainline railroad market not the industrial market. So it would be serviced in a roundhouse near a locomotive parts locker, by the same crews working on Alcos and EMDs... rather than in the field by the same crew who works on excavators and haul trucks.

I couldn't resist calculating the TBD resistor-it's about 372 ohms and watts, both. That's a TON of heat to deal with-also the standard warnings apply in that all parts of the system can be at 600v potential untill it is in normal operation, including what seems to be a 'loose' ground connection of some kind?

Looking theres not many 'stock' options for a resistor that size. do the streetcar guys wind their own? lol

Robert

Yes.

At WRM, we have rewound headlight dropping resistors. On Sacramento Northern 1005 the 120-volt headlight bulb is 250 watts, so we have about 2000 watts of resistance in series with it.

The resistor is a frame with six ceramic tubular cores which we rewound with nichrome wire.

I would hate to operate from the rear cab with a headlight on a summer night. The cab is about the size of a telephone booth, the door must be closed to operate, and the only ventilation would be an open cab window. That resistor is bigger than most residential portable space heaters!

It could be done with two or more stock power resistor tubes in series. say three tubes rated 175 or 225 Watts each at about 125 Ohms per tube. I'd have to check an Ohmite or MRC catalogue to be sure of the Ohmages available but it could be done with a variable type if the fixed types weren't available.

Gord

i believe a resistor of that size was discussed in the very first article in thus thread.